The present invention relates to a window sash positioner or sash balance and more particularly to a self-releasing friction operating device.
A basic problem encountered with window sashes designed to be raised and lowered by sliding within vertical jamb channels is that the windows tend to stick if the window sash is fitted too tightly against the corresponding jamb. Conversely, if the window sash is fitted loosely within the window jamb, the window will not remain in a raised position. Frequently, thus, this type of window either cannot be easily raised and lowered or it can not reliably be positioned in a variety of stationary positions.
With the advent of aluminum and like metal window sashes and casings, various frictional devices have been developed and employed to avoid the use of pulley and bias spring arrangements which are costly and complex. Typically, however, such frictional devices have one predominant shortcoming, i.e., the friction has been a constant factor existing when the sash is both raised and lowered. The friction must have a magnitude such as to exceed the weight of the window itself in order to hold the window in any desired raised position. The resistance of the positioner must be overcome when lowering the window; however, this is accomplished generally without undue difficulties since the weight of the window complements the downward force applied by the user. Raising of the window sash, however, requires the user to overcome a force exceeding both the weight of the window plus the frictional force applied by the window positioner. Thus, this has been a severe detriment to the use of such window positioners often compelling the use of more complicated and expensive devices which are easier to operate.
It has also been found that such prior window positioners must be provided in a variety of different sizes and designs for windows of different widths, weights, and heights therefore requiring the manufacturer to provide a variety of such devices for use with the various window types. The attachment of such devices to the window and the jamb has in many cases also significantly increased the cost of the assembled window, particularly, when the positioning device forms an integral part of the window sash or jamb.
A significantly improved window sash positioner is disclosed in a commonly assigned U.S. Pat. No. 3,788,006, issued Jan. 29, 1974 entitled SELF-RELEASING FRICTIONAL WINDOW SASH BALANCE. The window positioning device disclosed therein is adapted to be mounted between a movable window sash and a window jamb to provide a relatively low frictional force between the sash and the jamb as the window is raised and an increased holding frictional force once the window is in a desired raised position. The window positioner disclosed therein is secured to the window sash and is positioned within a generally U-shaped jamb channel having a pair of side walls. The window sash is narrower than the jamb assembly so that the positioning devices may be mounted on each side of the window and extend into opposite sides of the jamb channel. During assembly, the positioning devices are first attached to the window and the window is installed in the jamb by shifting the window sash to one side and resiliently flexing a mounting bracket for the positioner such that the positioner clears the sides of the jamb and is shifted into the jamb channels.
Although the apparatus described in the abovementioned commonly assigned patent was a significant improvement in window sash positioner devices, it remains desirable to provide a window sash positioner which can be installed simply and conveniently after the window sash is installed in the supporting jamb framework.